JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
ELECTRICAL ENGINEERING
STUDY OF MAXIMUM POWER POINT TRACKING
ALGORITHMS AND IDENTIFICATION OF PEAK
POWER USING COMBINED ALGORITHM FOR
PHOTOVOLTAIC SYSTEM
1
1
CHETAN HATKAR,
2
ROHAN HATKAR
M.E In VLSI & Embedded System, Dr. D. Y. Patil College Of Engineering Ambi, Pune
2
B. E. Electrical, AMGOI, Vathar, Kolhapur
ABSTRACT: There are many methods used to track maximum power point (MPP) of photo voltaic (PV) array.
This paper presents a study and review of different techniques of peak power point tracking algorithms for
photo voltaic array. In this paper proposed new combined algorithm for rapid tracking photovoltaic system .
There are two stages, first stage algorithm fast tracking and fine tracking in second stage. It has combination of
perturb and observe algorithm and current sweep. By using this combination drawback of this two types cancel
each other and give real maximum power point tracking in rapid changing environmental condition i.e.
temperature and solar radiation.
Keywords: Maximum power point tracking (MPPT), Perturb and observe (P & O), Current sweep,
Photovoltaic (PV).
1.
INTRODUCTION
Now days, power demand is one of the major problem in whole world. Due to unavailability of enough resource
to give power, so renewable energy sources such as solar energy, wind energy are widely used. Solar energy is
used for many applications such as battery charging, solar pumping, solar heating, home power supply, satellite
power system etc. which have pollution and maintenance free. But initial investment cost of solar equipment is
high, it require charger/ inverter for any application. Since solar array have low conversion efficiency. So
overall cost of system is reduced by designing converter which gives maximum efficiency of photovoltaic array.
Which call maximum power point tracker.[1]
Maximum power point tracker (MPPT) which tracks continuously maximum power point that point have
maximum voltage Vm and maximum current Im of photovoltaic array. Many MPPT algorithm have been studied
and developed such as fractional open circuit, fractional short circuit, current sweep, perturb and observe (P &
O), incremental conductance. The P & O algorithm is most commonly used to track MPP. Because of easy
implement track MPP. But practically this algorithm does not track real MPP on rapid changing environmental
condition i.e. solar radiation and temperature. Drawback of P&O is overcome by using incremental conductance
technique but this is complex algorithm and difficult to implement. [6] Current sweep technique gives fast
tracking but its require periodically track the MPP. Its fails when solar irradiation and temperature variation
happen.
This paper presents a new approach or propose algorithm that two stage algorithm. First stage fast tracking and
second stage fine tracking. It is combination of perturb and observe technique and current sweep MPP tracking
methods. The proposed algorithm identify quickly and accurately the MPP in non-ideal environmental
condition.
2.
PV MODULE AND CHARACTERISTICS
The equivalent circuit of a PV module is shown in Fig. 1(a), while typical output characteristics are shown in
Fig. 1(b). The characteristic equation for this PV model is given by [1],
ܸ + ‫ܴܫ‬ௌ
‫ݍ‬
൫V − ‫ܴܫ‬ௌ ൯൨ − 1ൠ −
I = ‫ܫ‬௅ீ − ‫ܫ‬ைௌ − ൜݁‫ ݌ݔ‬൤
ܴௌு
‫ܶ݇ܣ‬
where
‫ܧݍ‬
ܶ ଷ
1
1
‫ܫ‬ைௌ = ‫ܫ‬ை௥ ൤
൨ ݁‫ ݌ݔ‬൤ ீை ൬
− ൰൨
ܶ‫ݎ‬
‫݇ܤ‬
ܶ‫ݎ‬
ܶ
And
I and V
‫ܫ‬௅ீ = ൣ‫ܫ‬ௌ஼ோ + ‫ܭ‬1ሺܶ − 25ሻ൧ߣ/100
cell output current and voltage;
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IOS
T
k
q
KI=0.0017 A/oC
cell reverse saturation current;
cell temperature in oC;
Boltzmann’s constant;
electronic charge;
short circuit current temperature
coefficient at ISCR ;
λ
solar irradiation in W/m2 ;
ISCR
short-circuit current at 25oC and
1000 W/m2 ;
ILG
light-generated current;
EGO
band gap for silicon;
B=A=1.92
ideality factors;
Tr=301.18oK
K reference temperature;
Ior
cell saturation current at Tr ;
Rsh
shunt resistance;
Rs
series resistance.
The variation of the output I-V characteristics of a commercial PV module as function of temperature and
irradiation is shown in Fig. 2 (a) & (b) and Fig. 3(a) & (b), respectively. It is seen that the temperature changes
affect mainly the PV output voltage, while the irradiation changes affect mainly the PV output current. The
intersection of the load-line with the PV module I-V characteristic, for a given temperature and irradiation,
determines the operating point. The maximum power production is based on the load-line adjustment under
varying atmospheric conditions.
(a) Equivalent circuit of a PV module
Fig no. 1
(b) typical PV module current-voltage characteristics
(a)
(b)
Fig No.2 characteristic of a PV module with constant irradiation and varying temperature
(a)
(b)
Fig No. 3 Characteristics of a PV module with constant temperature and varying irradiation.
3.
PROBLEM OVERVIEW
PV module characteristics shows maximum power point at which has maximum voltage and maximum current.
MPPT algorithms tracks continuously that point in variation of solar irradiation and temperature also and under
partial shading condition.
MPPT Algorithm
We introduce different MPPT techniques below.
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1)
Fractional Open Circuit Voltage :Photovoltaic have near linear relationship between Vmmp and VOC
Vmpp ≈ K1 VOC
Where K1 is constant of proportionality, since K1 is dependent on characteristic of PV array. Factor K1 has
been in range between 0.71 to 0.78.[2],[4]
In this method VOC is calculated by disconnecting solar array from DC-DC converter. Then calculate the Vmmp
using K1 factor. So, this system have temporary loss power when it calculate VOC. K1 factor is no more valid
under partial shading condition and charging solar radiation.
2)
Fractional Short Circuit Current:Immp is also linearly function with ISC i.e. short circuit current of PV array.
Immp ≈ K2 ISC
Where K2 is proportionality constant. It has range in between 0.78 to 0.92. In this technique ISC is calculated by
periodically short circuit the PV array to track the Immp. This increases number of components and cost. .[2],[4]
3)
Perturb And Observe (P & O):P & O techniques work periodically incrementing or decrementing the voltage of PV array. The change in
power is observed. If perturbation has observed increases in PV power then it continuous to perturb in same
direction, if it is decreases then the perturb in opposite direction. See flow chart. P+ & O means it observe PV
power and compare new power with old power. According to that it increases or decreases duty cycle to gate
maximum power point. .[2],[4],[5]
P & O algorithm is simple to implement but in rapidly Changing solar radiation condition it oscillates around
MPP.
4)
Incremental conductance –
Drawback of P & O is overcome by incremental conductance technique. Incremental size decide fast tracking if
we use more size then it oscillate MPP & not track the exact MPP. The incremental conductance (IncCond)
method is based on the fact that the slope of the PV array power curve (Fig. 1(c)) is zero at the MPP, positive on
the left of the MPP, and negative on the right, as given by .[2],[3],[4]
dP/dV = 0 , at MPP
(1)
൝ dP/dV > 0 , ݈݂݁‫ ܲܲܯ ݂݋ ݐ‬
dP/dV < 0 , ‫݃݅ݎ‬ℎ‫ܲܲܯ ݂݋ ݐ‬
Since
݀ܲ ݀ሺ‫ܸܫ‬ሻ
݀‫ܫ‬
∆‫ܫ‬
(2)
=
=‫ܫ‬+ܸ
≈I+V
ܸ݀
ܸ݀
ܸ݀
∆ܸ
(1) can be rewritten as
∆I/∆V = 0 , at MPP
(3)
൝ ∆I/∆V > 0 , ݈݂݁‫ ܲܲܯ ݂݋ ݐ‬
∆I/∆V < 0 , ‫݃݅ݎ‬ℎ‫ܲܲܯ ݂݋ ݐ‬
Fig. 4. IncCond algorithm as shown in [2]
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The MPP can thus be tracked by comparing the instantaneous conductance (I/V ) to the incremental conductance
(∆I/∆V ) as shown in the flowchart in Fig. 4. Vref is the reference voltage at which the PV array is forced to
operate. At the MPP, Vref equals to VMPP. Once the MPP is reached, the operation of the PV array is
maintained at this point unless a change in ∆I is noted, indicating a change in atmospheric conditions and the
MPP. The algorithm decrements or increments Vref to track the new MPP.
5)
Current sweep The current sweep [2][8] method uses a sweep waveform for the PV array current such that the I V characteristic
of the PV array is obtained and updated at fixed time intervals. The VMPP can then be computed from the
characteristic curve at the same intervals. The function chosen for the sweep waveform is directly proportional
to its derivative as in
ௗ௙ሺ௧ሻ
݂ሺtሻ = ݇ସ
(1)
ௗ௧
Where ݇ସ is a proportionality constant. The PV array power is thus given by
P(t)=v(t)i(t)=(t)f(t)
(2)
At the MPP
ௗ௣ሺ௧ሻ
ௗ௩ሺ௧ሻ
ௗ௣ሺ௧ሻ
ௗ௩ሺ௧ሻ ௗ௙ሺ௧ሻ
= vሺtሻ + fሺtሻ
=0
ௗ௧
Substituting (1) in (3) gives
ௗ௧
(3)
= ቂvሺtሻ + ௗ௧ ቃ ௗ௧ = 0
(4)
The differential equation in (1) has following solution
݂ሺ‫ݐ‬ሻ = ‫ݐ[݌ݔ݁ܥ‬/݇ସ ]
(5)
C is chosen to be equal to the maximum PV array current Imax and k4 to be negative, resulting in a
decreasing exponential function with time constant τ = −k4. Equation (5) leads to
݂ሺ‫ݐ‬ሻ = ‫ܫ‬ெ஺௑ ݁‫[݌ݔ‬−‫ݐ‬/߬]
(6)
The current in (6) can be easily obtained by using some current discharging through a capacitor. Since the
derivative of (6) is nonzero, (4) can be divided throughout by df (t)/dt and, with f(t) = i(t), (4) simplifies to
ௗ௧
ௗ௣ሺ௧ሻ
ௗ௩ሺ௧ሻ
= vሺtሻ + ݇ସ
=0
(7)
ௗ௧
Once VMPP is computed after the current sweep, (7) can be used to double check whether the MPP has been
reached. In [2], the current sweep method is implemented through analog computation. The current sweep takes
about 50 ms, implying some loss of available power. In [2], it is pointed out that this MPPT technique is only
feasible if the power consumption of the tracking unit is lower than the increase in power that it can bring to the
entire PV system.
ௗ௜
4.
PROPOSED ALGORITHM FOR MPPT
Drawback of P & O is the performance of the Perturb and Observe depends on the sampling interval
and the duty-cycle perturbation of the algorithm . Those parameters set the dynamic response of the MPPT, such
as speed, accuracy and stability. The duty cycle step must be chosen properly. Since the Perturb and Observe
technique oscillates around the maximum power point, reducing the duty cycle step can minimize the oscillation
and the steady state losses. However, the controller is less efficient when the atmospheric conditions change
rapidly.
The current sweep method manipulates the solar panel current, so during the current sweep there will be reduced
power output. The current sweep determines the i-v characteristic of the solar panel and the maximum power
point voltage is determined. The controller holds this computed voltage as the operating voltage of the solar
panel until the next current sweep determines a new maximum power point voltage. So, the current sweep is not
performed continuously, but only periodical. It only makes sense to perform a current sweep if the increase in
generated power is greater than the loss of power by performing the current sweep. This is the main
consideration for determining the period of the current sweep method.[2],[4]
The proposed algorithm have two stage tracking that offer first stage fast tracking and fine tracking in the
second stage .If we combine Perturb and Observe & current sweep method it will be cancel out drawback of
each other.Current sweep method gives fast tracking & fine tracking by using P & O with proper duty step size
to track the MPPT. Proposed algorithm flow chart shown below Fig no. 5.
It is assumed that the PV module is operated at a given point. The algorithm commands the converter to make a
sweep in the modules characteristic. Make the sweep which duty cycle vary 10% to 90% . At this sweep time
duration PV_V & PV_I sensed to calculate PV power. In controller make the array for sweep duration which
has calculated PV power for each duty %(10% to 90%). Find largest power in that array ,that point is MPP, that
power duty used for mpp tracking. Due to drawback of current sweep is not performed continuously, but only
periodically use timer for 5 min duration to track MPP continuously but rapid clouds may be present, thus the
MPP may change faster than the ‘normal operating period’. Besides, if the sweep-duration is too long, the
irradiance may have changed and the recorded curve corresponds to two different irradiations. To avoid this use
P & O algorithm here. After staring ON the timer for 5 min in this duration use P & O algorithm. It compare
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new power with old power according to that duty cycle will be increase & decrease to by using proper duty
cycle step size to get fine tracking of MPP.
Fig No.5: flow chart of Proposed algorithm
After completing 5 min make the next current sweep to get new MPP & this cycle is repeated for every 5 min.
5.
CONCLUSION
The proposed algorithm gives two necessary factor in finding out real maximum power point which are rapid
tracking response in rapid changing of climate conditions of solar radiation & temperature compare to
traditional algorithm.
The proposed algorithm cancel out the drawback of P & O algorithm & current sweep each other when this
two algorithm
lgorithm used in combine form to achieve fast tracking of maximum power point for photovoltaic syatem.
6. REFERENCES
[1] Eftichios Koutroulis, Kostas Kalaitzakis,
Kalaitzakis Member, IEEE,, and Nicholas C. Voulgaris “Development of a
Microcontroller-Based, Photovoltaicc Maximum Power Point Tracking
Control System”, IEEE
TRANSACTIONS ON POWER ELECTRONICS, VOL. 16, NO. 1, JANUARY 2001
[2] Trishan Esram,, Student Member, IEEE
IEEE, and Patrick L. Chapman, Senior Member, IEEE “ Comparison of
Photovoltaic Array Maximum Power Point
Point Tracking Techniques” IEEE TRANSACTIONS ON ENERGY
CONVERSION, VOL. 22, NO. 2, JUNE 2007
JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
ELECTRICAL ENGINEERING
[3] Moacyr Aureliano Gomes de Brito, Luigi Galotto, Jr., Leonardo Poltronieri Sampaio, Guilherme de Azevedo
e Melo, and Carlos Alberto Canesin, Senior Member IEEE “Evaluation of the Main MPPT Techniques for
Photovoltaic Applications” IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 60, NO. 3,
MARCH 2013
[4] D. P. Hohm and M. E. Ropp*,y Electrical Engineering Department, South Dakota State University,
Brookings, SD 5700-2220, USA “Comparative Study of Maximum Power Point Tracking Algorithms”
PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS Prog. Photovolt: Res. Appl. 2003.
[5] Nicola Femia, Member, IEEE, Giovanni Petrone, Giovanni Spagnuolo, Member, IEEE, and Massimo Vitelli
“Optimization of Perturb and Observe Maximum Power Point Tracking Method” IEEE TRANSACTIONS ON
POWER ELECTRONICS, VOL. 20, NO. 4, JULY 2005
[6] Dzung Phan Quoc, Quang Nguyen Nhat, Phuong Le Minh, Khoa Le Dinh, Vu Nguyen Truong Dan and Anh
Nguyen Bao Faculty of Electrical & Electronic Engineering, HCMC University of Technology, Ho Chi Minh
City, Vietnam Hong Hee Lee chool of Electrical Engineering, University of Ulsan, Ulsan, Korea “The New
Combined Maximum Power Point Tracking Algorithm Using Fractional Estimation in Photovoltaic Systems”
IEEE PEDS 2011, Singapore, 5 - 8 December 2011.
[7] Sachin Jain, Student Member, IEEE, and Vivek Agarwal, Senior Member, IEEE “A New Algorithm for
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ELECTRONICS LETTERS, VOL. 2, NO. 1, MARCH 2004.
[8] Ofualagba Godswill , Onyan Aaron Okiemute , Igbinoba Kevwe Charles “Design of Maximum Power Point
Tracker (MPPT) and Phase Locked Loop (PLL) in a PV-Inverter”International Journal of Engineering Research
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